The significance of evolutionary fitness in natural selection lies in its role in determining how well organisms adapt to their environments. Evolutionary fitness refers to an organism's ability to survive, reproduce, and pass on its genes to the next generation. Those individuals with traits that enhance their chances of survival and reproduction are more likely to contribute to the next generation, leading to the propagation of advantageous characteristics. Understanding fitness helps explain the mechanisms of adaptation and the evolutionary changes that occur within populations over time as they respond to environmental pressures.